The present invention relates to an image-forming material utilizing the coloring (or decoloring) reaction with an acid.
Also, the invention relates to an image-forming material having a coloring layer containing an acid-generating agent generating an acid by the action of heat and a compound forming a light-absorption change by the reaction with an acid, having a high sensitivity, and having a good shelf life.
Furthermore, the invention relates to a sulfonic acid ester derivative that is decomposed by the action of heat, light, etc., to generate an acid.
Also, the invention relates to a sulfonic acid ester derivative that is excellent in the shelf life and efficiently generates an acid by the action of heat, light, etc.
Still further, the invention relates to a novel sulfonic acid derivative capable of providing an image-forming material excellent in the sensitivity, the image quality, the shelf life, etc., by using together with a compound causing changes in the light-absorption, the hydrophilic or hydrophobic property, etc., by the reaction with an acid.
Sulfonic acid esters have been widely used as various reactants, etc., in organic syntheses. Also, by utilizing the property of a sulfonic acid ester that the ester is decomposed to generate sulfonic acid, the sulfonic acid ester is used as an acid-generating agent in the field of image formation.
As the acid-generating agent, compounds each generating an acid by the action of heat, light, etc., are known and properly used according to the purposes used. In these compounds, in regard to an acid-generating agent upon heating generating an acid by the action of heat, it is necessary that the storage stability of being not decomposed by heat during storage with the passage of time is compatible with the activity for the acid-generating reaction by heat, or if it is insufficient, the distinguishing property of the region received heat or light and the region of not received heat or light is lowered. Hitherto, the investigation of improving the compatibility of this kind of shelf life with the reactivity of the acid-generating agent upon heating has been made, and the outline thereof is summarized in xe2x80x9cYuki Zairyo (Organic materials) for imagingxe2x80x9d (1997) edited by Organic Electronics Material Kenkyu Kai (Research Society) (published by Bunshin Shuppan K.K.), but the content is yet very insufficient in the above-described point, and further improvements have been desired.
Also, recently, with the progress of high-output lasers, the investigations of image-recording media of heat mode using these lasers have been actively carried out. A method of generating an acid by irradiating a laser using a high-output laser and forming images by the acid and a dye precursor is disclosed in EP-A-0909656, but in the method, because in the case of using a high-output laser, the surface of an image-recording medium is partially thermally broken (so-called abrasion), a haze is increased and background staining, etc., are caused, there is a restriction in the increase of a reaction temperature. As the result thereof, the compatibility of the reactivity with the storage stability, that is, the distinguishability as a recording material is also insufficient in a recording system using a laser light, and the developments of the image-recording method and materials having the compatibility for practical use have yet become a problem in the field of imaging technology.
A 1st object of the present invention is to provide a novel image-forming material having a high sensitivity and being excellent in the storage stability.
A 2nd object of the invention is to provide an image-forming material giving a low haze and a good surface state even in the case of forming images using a high-output laser.
A 3rd object of the invention is to provide a sulfonic acid ester derivative, which is decomposed by the action of heat, light, etc., to generate an acid.
A 4th object of the invention is to provide a sulfonic acid derivative that is excellent in the shelf life and efficiently generates an acid by the action of heat, light, etc.
A 5th object of the invention is to provide a novel sulfonic acid derivative capable of providing an image-forming material excellent in the sensitivity, the image quality, the shelf life, etc., by using together with a compound which causes changes of the light-absorption, the hydrophilic of hydrophobic property, etc. by the reaction with an acid.
As the result of various investigations for attaining the above-described 1st and 2nd objects, the present inventor has found sulfonic acid group-containing compounds which are stable during the storage and effectively generates an acid by the action of heat and light and also found that by using the compound as an acid-generating agent, the objects can be attained. That is, it has been found that the above-described 1st and 2nd objects have been attained by the 1st to 6th aspects of the invention shown below.
Furthermore, it has also been found that the above-described 3rd, 4th, and 5th objects has been attained by the sulfonic acid ester derivative described in the 7th to 9th aspects of the invention shown below.
That is, the 1st aspect of the invention is an image-forming material comprising on a support the acid-generating agent represented by following formula (I) generating an acid by the action of heat or a polymer obtained by copolymerizing the acid-generating agent and a compound causing a change in the absorption region of from 360 to 700 nm by an intramolecular or intermolecular reaction by the action of an acid, 
wherein R1 represents an alkyl group, an aryl group, or a heterocyclic group, R2 and R3 each independently represents an alkyl group or an aryl group, excluding that R2 and R3 are simultaneously aryl groups, R2 and R3 may combine to form a ring, and at least one of R2 and R3 has a polymerizing unsaturated group.
The 2nd aspect of the invention is the image-forming material as described in the above-described 1st aspect, wherein the acid-generating agent represented by the above-described formula (I) is represented by following formula (II): 
wherein R1 has the same meaning as in the formula (I), X represents an atomic group necessary for forming a ring together with C, and at least one of the atomic group constituting X has a polymerizing unsaturated group.
The 3rd aspect of the invention is the image-forming material as described in the above-described 1st or 2nd aspect, wherein the material comprises a polymer having, as a repeating unit, a partial structure having an acid-generating function obtained by polymerizing the acid-generating agent represented by the formula (I) or (II).
The 4th aspect of the invention is the image-forming material as described in the above-described 3rd aspect, wherein the polymer as described in the 3rd aspect is a polymer represented by following formula (III):
xe2x80x94(A)xxe2x80x94(B)yxe2x80x94(C)zxe2x80x94xe2x80x83xe2x80x83(III) 
wherein A represents a repeating unit obtained by polymerizing the acid-generating agent represented by the formula (I) or (II), B represents a repeating unit obtained by polymerizing at least one kind of a vinyl monomer having a partial structure causing a change in the absorption region of from 360 to 700 nm by the action of an acid, C represents a repeating unit obtained by polymerizing at least one kind of a vinyl monomer polymerizable with A and B, x, y and z represent mol %, each is 1xe2x89xa6xxe2x89xa6100, 0xe2x89xa6yxe2x89xa699, 0xe2x89xa6zxe2x89xa699, and x+y+z=100.
The 5th aspect of the invention is the image-forming material as described in the above-described 1st to 4th aspects, wherein the image-forming material comprises an infrared absorbing dye and forms images by irradiation of an infrared laser light.
The 6th aspect of the invention is the image-forming material as described in the above-described 1st to 5th aspects, wherein the image-forming layer does not comprise therein a silver compound or the salt thereof.
The 7th aspect of the invention is a sulfonic acid ester derivative represented by following formula (I): 
wherein R1 represents an alkyl group, an aryl group, or a heterocyclic group, R2 and R3 each independently represents an alkyl group or an aryl group, excluding that R2 and R3 are simultaneously aryl groups, R2 and R3 may combine to form a ring, and at least one of R2 and R3 has a polymerizing unsaturated group.
The 8th aspect of the invention is the sulfonic acid derivative as described in the above-described 7th aspect, wherein the sulfonic acid ester derivative represented by the above-described formula (I) is represented by following formula (II): 
wherein R1 has the same meaning as in the formula (I), X represents an atomic group necessary for forming a ring together with C, and at least one of the atomic group constituting X has a polymerizing unsaturated group.
The 9th aspect of the invention is a polymer obtained by polymerizing the sulfonic acid material represented by the formula (I) of the above-described 7th aspect or the formula (II) of the above-described 8th aspect.
Then, the invention is described in detail.
In the formula (I) described above, R represents an alkyl group (methyl, ethyl, n-propyl, isopropyl, t-butyl, n-octyl, dodecyl, cyclopropyl, cyclopentyl, cyclohexyl, [0,1,3]bicyclohexyl, [1,2,2]bicycloheptyl, [1,1,3]bicycloheptyl, etc.), an aryl group (phenyl, naphthyl, etc.), or a heterocyclic group (furyl, thienyl, pyrimidinyl, benzothiazolyl, etc.). In these groups, an alkyl group or an aryl group are preferred and an aryl group is particularly preferred. These groups have from 1 to 18 carbon atoms, and preferably from 1 to 12 carbon atoms excluding a substituent.
Also, these groups each may further have a substituent, as the substituent, any substituent by which a hydrogen can be substituted may be used, and the preferred examples of the substituents include a halogen atom (e.g., fluorine, chlorine, bromine, and iodine), an alkyl group (practically same as described above and further includes a cycloalkyl group and a bicycloalkyl group), an alkenyl group (vinyl, allyl, prenyl, geranyl, oleyl, 2-cyclopenten-1-yl, etc.), an alkinyl group (ethynyl, propargyl, trimethylsilylethynyl, etc.), an aryl group (practical examples are same as described above), a heterocyclic group (practical examples are same as described above), a cyano group, a hydroxyl group, a nitro group, a carboxyl group, an alkoxy group (methoxy, ethoxy, isopropoxy, t-butoxy, n-octyloxy, etc.), an aryloxy group (phenoxy, naphthoxy, etc.), a silyloxy group (trimethylsiyloxy, t-butyldimethylsilyloxy, etc.), a heterocyclic group (pyridyloxy, 2-tetrahydropyranyloxy, etc.), an acyloxy group (formyloxy, acetyloxy, pivaloyloxy, stearoyloxy, benzoyloxy, etc.), a carbamoyloxy group (N,N-dimethylcarbamoyloxy, morpholinocarbonyloxy, N,N-di-n-octylaminocarbonyloxy, N-n-octylcarbamoyloxy, etc.), an alkoxycarbonyloxy group (methoxycarbonyloxy, ethoxycarbonyloxy, t-butoxycarbonyloxy, n-octylcarbonyloxy, etc.), an aryloxycarbonyloxy group (phenoxycarbonyloxy, etc.), furthermore, an amino group (including an anilino group, amino, methylamino, dimethylamino, anilino, N-methylanilino, diphenylamino, etc.), an acylamino group (acetylamino, pivaloylamino, lauroylamino, benzoylamino, 3,4,5-tri-n-octyloxyphenyl-carbonylamino, etc.), a carbamoylamino group (carbamoylamino, N,N-dimethylaminocarbonylamino, N,N-diethylcarbonylamino, morpholinocarbonylamino, etc.), an alkoxycarbonylamino group (methoxycarbonylamino, ethoxycarbonylamino, t-butoxy-carbonylamino, n-octadecyloxycarbonylamino, N-methyl-methoxycarbonylamino, etc.), an aryloxycarbonylamino group (phenoxycarbonylamino, etc.), a sulfamoylamino group (sulfamoylamino, N,N-dimethylaminosulfonylamino, N-n-octylaminosulfonylamino, etc.), an alkyl- and arylsulfonylamino group (methylsulfonylamino, butylsulfonylamino, phenylsulfonylamino, etc.), moreover, a mercapto group, an alkylthio group (methylthio, ethylthio, n-hexadecylthio, etc.), an arylthio group (phenylthio, etc.), a heterocyclic thio group (2-benzothiazolylthio, 1-phenyltetrazol-5-ylthio, etc.), a sulfamoyl group (N-ethylsulfamoyl, N-(3-dodecyloxypropyl)sulfamoyl, N,N-dimethylsulfamoyl, N-acetylsulfamoyl, N-benzoylsulfamoyl, N-(Nxe2x80x3-phenylcarbamoyl)sulfamoyl, etc.), a sulfo group, an alkyl- and arylsulfinyl group (methylsulfinyl, ethylsulfinyl, phenylsulfinyl, etc.), an alkyl- and arylsulfonyl group (methylsulfonyl, ethylsulfonyl, phenylsulfonyl, etc.), an acyl group (acetyl, pivaloyl, 2-chloroacetyl, stearoyl, benzoyl, etc.), an aryloxycarbonyl group (phenoxycarbonyl, etc.), an alkoxycarbonyl group (methoxycarbonyl, ethoxycarbonyl, t-butoxycarbonyl, n-octadecyloxycarbonyl, etc.), a carbamoyl group (carbamoyl, N-methylcarbamoyl, N,N-dimethylcarbamoyl, N,N-di-n-octylcarbamoyl, N-(methylsulfonyl)carbamoyl, etc.), an imido group (N-succinimide, N-phthalimide, etc.), a phosphino group (dimethylphosphino, diphenylphosphino, etc.), a phosphinyl group, a phosphinyloxy group, a phosphinylamino group, and a silyl group (trimethylsilyl, t-butyldimethylsilyl, phenyldimethylsilyl, etc.). These substituents may be further substituted by the above-described substituents.
As the substituent of R1, an alkyl group is most preferred.
Practical examples of R1 are shown below, but the invention is not limited to these examples. 
In the above formulae, * shows the position for bonding with xe2x80x94SO3xe2x80x94 in the formula (I) or the formula (II), and so forth. 
In the formula (I), R2 and R3 each independently represents an alkyl group or an aryl group but it is excluded that R2 and R3 are simultaneously aryl groups. Examples of the alkyl group and the aryl group are same as those described about R1. R2 and R3 each may further have a substituent and the preferred examples of the substituent are those illustrated above as the substituents of R1. Also, at least one of R2 and R3 has a polymerizing unsaturated group. As the polymerizing unsaturated group, a vinyl group is preferred.
Also, R2 and R3 may combine to form a ring. As examples of the sulfonic acid ester of the invention wherein R2 and R3 form a ring, there are various compounds, and the preferred modes thereof are those represented by the formula (II) described above.
In the formula (II), R1 has the same meaning as those in the formula (I). X represents an atomic group necessary for forming a ring together with C and has at least one polymerizing unsaturated group. The polymerizing unsaturated group has the same meaning as those described in the explanation of the formula (I). X forms a ring together with C as described above, as the ring, a 3- to 8-membered rings are preferred, 5- or 6-membered ring is more preferred, and a 6-membered ring is particularly preferred. X is preferably a non-metallic atomic group and more preferably an atomic group formed by linearly bonding plural divalent groups selected from xe2x80x94C(R4)(R5)xe2x80x94, xe2x80x94C (xe2x95x90Y)xe2x80x94, xe2x80x94N(R6)xe2x80x94, xe2x80x94Oxe2x80x94, and xe2x80x94Sxe2x80x94 and these plural divalent groups may be the same or different. The preferred divalent group is xe2x80x94C(R4)(R5)xe2x80x94. Wherein, R4, R5, and R6 each represents a hydrogen atom or a substituent and preferred examples of the substituent are same as those described above in the explanation of R1. When plural ones of R4, R5, or R6 exist in a molecule, they may be the same or different and also two or more of R4, R5, or R6 may combine to form a ring, Y represents xe2x95x90O, xe2x95x90S, or xe2x95x90Nxe2x80x94R6 wherein R6 has the same meaning as those explained above about xe2x80x94N(R6)xe2x80x94.
Also, in the compounds represented by the formula (II), more preferred compounds are the compounds represented by following formula (IV). 
wherein R1 has the same meaning as that in the formula (I), R7 represents a hydrogen atom or an alkyl group, the alkyl group may further have a substituent, and the practical examples of the alkyl group and the substituent are same as those described as the practical examples of R1. R7 is preferably a hydrogen atom or a methyl group.
In the compounds represented by the formulae (I), (II), and (IV), there are compounds wherein isomers such as cis-form isomers, trans-form isomers, etc., exist, and in the invention, they are not specified and also the case of using them as a mixture is included in the invention.
Also, as practically described below in synthesis examples, each of these compounds can be synthesized by the dehydrochlorination of a compound having a hydroxy group and sulfonyl chloride and, in succession, reacting the product and a polymerizing group-containing acyl chloride or after dehydrochlorinating the compound having a hydroxy group and the polymerizing group-containing acyl chloride, by reacting the product and sulfonyl chloride.
Then, polymer compounds induced from the compounds each having a polymerizing group are explained.
When by polymerizing the compounds represented by the formulae (I), (II), and (IV), they show more large ability as functional materials. The molecular weights of the polymers of the invention are preferably in the range of from 1,000 to 1,000,000, and particularly preferably in the range of from 2,000 to 100,000.
The synthesis of the polymer of the invention can be carried out by various polymerization methods such as a solution polymerization, a precipitation polymerization, a suspension polymerization, a bulk polymerization, and an emulsion polymerization. Also, as the initiation method of the polymerization, there are, for example, a method of using a radical initiator and a method of irradiating a light or a radiation. These polymerization methods and the imitation methods of the polymerizations are described, for example, in Teiji Tsuruta, xe2x80x9cHigh Molecule Synthesis Methodxe2x80x9d, revised edition, (published by Nikkan Kogyo Shinbun Sha, 1971) and Takayuki Ootsu and Masaetsu Kinoshita, xe2x80x9cExperiment Method of High Molecule Synthesisxe2x80x9d published by Kagaku Doojin, 1972, pages 124 to 154.
In the above-described polymerization methods, the solution polymerization method using a radical initiator is particularly preferred. As the solvent used for the solution polymerization, there are, for example, various organic solvents such as ethyl acetate, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetone, dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, benzene, toluene, acetonitrile, methylene chloride, chloroform, and dichloroethane, and these organic solvents may be used singly or as a mixture of two or more kinds thereof, or further may be used as a mixed solvent with water.
It is necessary that the polymerization temperature is established in connection with the molecule weight of the polymer formed, the kind of the initiator, etc., and the polymerization can be carried out at various temperatures but usually the polymerization is carried out at a temperature of from 30 to 100xc2x0 C. In the invention, it is preferred to carry out the polymerization at a temperature range of from 30 to 90xc2x0 C.
As the radical initiator used for the polymerization, for example, azo-base initiators such as 2,2xe2x80x2-azobis-isobutyronitrile, 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile), 2,2xe2x80x2-azobis(2-amidinopropane) dihydrochloride, and 4,4xe2x80x2-azobis(4-cyanopentanoic acid) and peroxide-base initiators such as benzoyl peroxide, t-butyl hydroperoxide, and potassium persulfate (for example, it may be used as a redox initiator by combining with sodium hydrogensulfite) are preferred. In the invention, the initiator wherein the temperature at which the half-life becomes 10 hours is not higher than 70xc2x0 C. (for example, 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile), 2,2xe2x80x2-azobis(4-methoxy-2,4-dimethylvaleronitrile), dimethyl-2,2xe2x80x2-azobis(2-methyl propionate), and 2,2xe2x80x2-azobis[2-(3,4,5,6-tetrahydropropane) dihydrochloride] are particularly preferred.
The using amount of the polymerization initiator can be controlled according to the polymerizing property of the monomer used and the molecule weight of the polymer required but is preferably in the range of from 0.01 to 5.0 mol % to the monomer.
Then, practical examples of the compound represented by the formula (I), the formula (II), or the formula (IV) are shown below but the invention is not limited to these compounds. In addition, the number of the homopolymer obtained by polymerizing the monomer shown below is shown by adding P- to the number of the monomer (for sample, the homopolymer of the illustrated compound (1) is shown (P-1). Others are also shown similarly). Also, in some monomers, isomers such as a cis-form isomer, a trans-form isomer, etc., exist, and the cases of polymerizing these mixtures are included in the invention.
Also, the addition amount of the acid-generating agent differs according to the kind of the compound showing the change of a light absorption used in the invention but, generally speaking, is preferably in the range of from 0.001 to 20 equivalents, and particularly preferably in the range of from 0.01 to 5 equivalents to the compound showing the change of the light absorption region of from 360 to 700 nm by the action of an acid described below.
Then, the compound causing the change of the light absorption of from 360 to 700 nm by causing the intramolecular or intermolecular reaction by the action of an acid is explained.
The compound of accompanying such a light absorption change may be a single compound or may be composed of two or more components. For example, there are (a) a combination of the compounds each forming a fading image in the above-described region by a Diels-Alder reaction (for example, a combination of 9,10-distyrylanthracene and maleic anhydride, a combination of tetraphenylcyclopentadiene and an acrylic acid ester, etc.), (b) a compound forming a color image in the above-described region by a Retrodiels-Alder reaction (for example, an addition product of 9,10-distyrylanthracene and maleic anhydride, an addition product of diphenylisobenzofuran and acrylamide, etc.), (c) a compound forming a color image in the above-described region by spreading of the conjugated system by releasing xcex2-hydrogen (for example, 1-acetoxy-1,2-diarylethane, 1-sulfoxy-1,2-diarylethane, etc.), (d) a combination of an aldehyde forming a color image in the above-described region by a dehydration condensation and an active methylene compound (for example, a combination of a four-equivalent magenta coupler for photography (pyrazolone derivative) and p-methoxycinnamaldehyde) and (e) a compound having an amino group or a hydroxyl group substituted by a substituent the decomposition or releasing of which is accelerated by the action of an acid in the molecule, and changing the light absorption in the above-described absorption region by the decomposition or the release of the above-described substituent.
The substituent of the amino group in the above-described compound of changing the light absorption by decomposing or releasing the substituent of the amino group by the action of an acid includes an alkoxycarbonyl group (e.g., t-butoxycarbonyl, cyclohexyloxycarbonyl, 2-(2-methyl)butoxycarbonyl, 2-(2-phenyl)propyloxycarbonyl, and 2-chloroethoxycarbonyl), an acyl group (e.g., acetyl, benzoyl, 2-nitrobenzoyl, 4-chlorobenzoyl, and 1-naphthyl) and a formyl group, but in the invention, an alkoxycarbonyl group having a hydrogen atom at the xcex2-position is particularly useful in the view points of the storage stability and the heat sensitivity.
Such compounds are described, for example, in U.S. Pat. Nos. 4,602,263 and 4,826,976, and by combining the compound with the acid-generating agent upon heating of the invention and the acid increasing agent, a heat-sensitive image-forming material having a high sensitivity and being excellent in the shelf life can be provided.
The substituent of the hydroxyl group in the compound changing the light-absorption by the decomposition or the release of the substituent of the hydroxyl group by the action of an acid preferably includes a secondary or tertiary alkoxycarbonyl group having a hydrogen atom at the xcex2-position (e.g., t-butoxycarbonyl, isopropyloxycrbomyl, 1-phenylethoxycarbonyl, 1,1-diphenylethoxycarbonyl, and 2-cyclohexeneoxycarbonyl), a silyl group (e.g., trimethylsilyl, triethylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl, and phenyldimethylsilyl), an alkoxymethyl group (e.g., methoxymethyl, ethoxymethyl, 1-methoxyethyl, 1-phenoxyethyl, and 2-(2-methoxypropyl)), and a secondary or tertiary alkyl group having a hydrogen atom at the xcex2-position (e.g., tetrahydropyranyl, tetrahydrofuranyl, 4,5-dihydro-2-methylfuran-5-yl, t-butyl, and 2-cyclohexenyl), but in the invention, the secondary or tertiary alkoxycarbonyl group having a hydrogen atom at the xcex2-position is particularly preferred. Examples of the compound changing the light absorption by the decomposition of the substituent of the hydroxyl group are described in U.S. Pat. No. 5,243,052 and JP-A-9-25360 (the term xe2x80x9cJP-Axe2x80x9d as used herein refers to as an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), etc.
Also, a basic leuco dye, etc., instantly coloring by the contact with an acid can be used in the image-forming material. As examples of such a compound, there are compounds described in xe2x80x9cImaging Organic Materialxe2x80x9d edited by Yuki (Organic) Electronics Material Kenkyu Kai, published by Bunshin Shuppan Sha (1997) and compounds described in the cited literatures described therein. Also, the compounds described in Japanese Patent Application Nos. 2000-62402 and 2000-65210 show a high coloring efficiency under the existence of an acid and can be preferably used in the invention.
Then, practical examples of the compound causing the change of the light absorption in the absorption region of from 360 to 700 nm by the action of an acid are shown below, but the invention is not limited to these compounds. 
The image-forming material of the invention is generally prepared by coating a solution containing the above-described acid-generating agent and the compound causing the change of the light absorption in the absorption region of from 360 to 700 nm by the action of an acid on a support. In this case, excluding the case that one of them is a polymer or that one of them is an amorphous having a coating property, usually a binder is used together. When the use of a binder is unnecessary, there are merits that the film thickness is liable to be thin and images having good definition are obtained.
Also, when a binder is used, a water-soluble binder such as gelatin, casein, starches, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, an ethylene-maleic anhydride copolymer, etc., or a water-insoluble binder such as polyvinyl butyral, triacetyl cellulose, polystyrene, a methyl acrylate-butadiene copolymer, an acrylonitrile-butadiene copolymer, etc., can be used.
On the other hand, one or both (including copolymer) of the acid-generating agent and the compound causing the change of the light absorption in the absorption region of from 360 to 700 nm by the action of an acid, the addition of a binder is unnecessary. In this case, a high sensitization can be expected in the meaning of generating an acid in the very vicinity of the compound. Also, by controlling the diffusion of the molecule(s) by the polymerization thereof, there is a possibility of improving the resolution and the shelf life of images. These characteristics are particularly preferred for the use of requiring a high image quality such as a graphic art film. A preferred mode of such a compound is represented by the formula (III) described above.
Then, the formula (III) is explained.
In the formula (III), A represents a compound shown by the formula (I), (II), or (IV).
In the formula (III), B represents a repeating unit obtained by the polymerization of at least one kind of a vinyl monomer having the partial structure causing a change of the light absorption in the absorption region of from 360 to 700 by the action of an acid. The compound causing the change of the light absorption by the action of an acid is as described above, and the vinyl monomer relating to B is the compound having introduced a polymerizing group to the position capable of being substituted in the above-described structure. Then, the practical examples thereof are shown below, but the invention is not limited to these compounds. 
In the formula (III), C represents a repeating unit obtained by the polymerization of at least one kind of a vinyl monomer capable of forming a copolymer with A and B, and by controlling the polarity, the glass transition temperature, etc., thereof, the storage stability, the coloring property, etc., can be controlled. Such vinyl monomers may be used as the combination of two or more kinds of them. As the preferred examples thereof, there are acrylic acid esters, methacrylic acid esters, acrylamide, styrene, and vinyl ethers.
Then, practical examples of the monomer constituting C are shown below but the invention is not limited to them. 
In the formula (III), x, y, and z represent mol % of each composition. Also, x, y, and z each is 1xe2x89xa6xxe2x89xa6100, 0xe2x89xa6yxe2x89xa699, and 0xe2x89xa6zxe2x89xa699, and x+y+z=100. Furthermore, z is preferably 0xe2x89xa6zxe2x89xa690, and more preferably 0xe2x89xa6zxe2x89xa650.
The molecular weight of the polymer represented by the formula (III) is in the range of preferably from 1,000 to 1,000,000, and particularly preferably from 2,000 to 100,000. Also, the polymer may be a homopolymer, a random copolymer, an alternating copolymer, a block copolymer, etc., but a homopolymer and a random copolymer, which can be easily synthesized, are preferred.
Then, preferred combinations of the monomers forming A, B, and C in the polymers represented by the formula (III) and x, y, and z are shown in Table 1 below, but the invention is not limited to these combinations.
The syntheses of these polymers are as described in the explanations of the formulae (I), (II), and (IV).
In the synthesis of the polymer represented by the formula (III) the monomers forming A, B, and C respectively are mixed and first placed in a reaction vessel and an initiator may be added thereto, or the polymerization may be carried out through the course of adding dropwise the monomers to a polymerization solvent.
The polymer represented by the formula (III) in the invention is a polymer having together a partial structure having a function of generating an acid by the action of heat or an acid and a partial structure causing the change of the light absorption in the absorption region of from 350 to 700 nm by the action of acid. As such a polymer, there can exist a polymer of a single monomer having both the functions described above, but from the view point of the synthesis, the polymer represented by the formula (III) is advantageous and the polymer represented by the formula (III) is preferred because the selective range of the monomers to be used is widened.
The image-forming material of the invention is generally prepared by coating polymer represented by the formula (III) on a support. When the polymer of the invention has a function of generating an acid by the action of heat, the change of the light absorption is independently caused in the absorption region by only the action of heat, whereby when the polymer is used for a heat-sensitive image-forming material, the sensitivity and the resolution of the image formed are excellent. Also, because in the image-forming material of the invention, the above-described polymer itself has a function of a binder, the binder as described above may not be used, whereby there are advantages that the film thickness can be thinned, images having a good resolution are obtained, and a thermal breakage, that is, an abrasion is hard to occur. However, in the case of using the polymer represented by the formula (III), if necessary, a binder may be used and as the practical examples of the binder, there are those described above.
In the present invention, for the purpose of increasing the storage stability of the image-forming material, a small amount of a base can be added, for the purpose of increasing the sensitivity, a compound generating an acid by the action of light or heat can be additionally added, and, if necessary, various additives such as a pigment, an antioxidant, a sticking inhibitor, etc., can be added. Also, for protecting the image-forming layer, an overcoat may be formed and a backcoat layer may be formed on the back surface of the support. In addition, various known techniques in heat-sensitive image-forming materials, such as a single layer or plural layers of undercoat layers containing a pigment or made of a resin are formed between the image-forming layer and the support.
In the case of using a protective layer in the invention, there is no particular restriction on a binder used for the protective layer if it is colorless and is a medium forming a transparent or translucent film and examples of the binder include water-soluble binders such as gelatin, casein starches, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, an ethylene-maleic anhydride copolymer, etc., and water-insoluble binders such as polyvinylbutyral, triacetyl cellulose, cellulose acetate butyrate, polyesters, polycarbonates, polyvinylesters (polyvinyl acetate, etc.), polystyrene, polyvinyl chloride, an acrylic acid ester and methacrylic acid ester polymer or copolymer (e.g., a methyl methacrylate-hydroxymethyl methacrylate copolymer, a methyl acrylate-butadiene copolymer, polymethyl methacrylate, poly t-butyl methacrylate, and an acrylonitrile-butadiene copolymer), etc.
In these binders, the water-insoluble binders are preferably used. The water-insoluble binder may form a film from a solution in an organic solvent or may form a film in the form of an aqueous dispersion. In this case, the aqueous dispersion is a dispersion formed by dispersing the water-insoluble hydrophobic polymer in a water-soluble dispersion medium as fine particles. As the dispersed state, there are states that the polymer is emulsified in the dispersion medium, the polymer is emulsion polymerized, the polymer is micelle-dispersed in the dispersion medium, the polymer partially has a hydrophilic structure in the molecule, and the molecule chain itself is dispersed in a molecular form, etc. These examples are described in xe2x80x9cSynthetic Resin Emulsionxe2x80x9d edited by Taira Okuda and Hiroshi Inagaki, published by Kobunshi Kanko Kai (1978), xe2x80x9cApplication of Synthetic Latexxe2x80x9d, edited by Takaaki Sugimura, Yasuo Kataoka, Soichi Suzuki, and Keiji Kasahara, published by Kobunshi Kanko Kai (1993), Soichi Muroi, xe2x80x9cChemistry of High-Molecular Latexxe2x80x9d, published by Kobunshi Kanko Kai (1970), etc. The mean particle size of the dispersed particles is in the range of preferably from 1 to 50,000 nm, and more preferably from about 5 to 1,000 nm. There is no particular restriction on the particle size distribution of the dispersed particles, and the dispersed particles may have a wide particle size distribution or a monodispersed particle size distribution.
The molecular weight of the polymer for the image-forming material and the protective layer is from 1,000 to 1,000,000, and preferably from about 20,000 to 500,000 as a weight average molecular weight. Also, the polymers may be used singly or, if necessary, as a blend of two or more kinds thereof.
Also, by controlling the Tg of the polymer used for the image-forming material and the protective layer, the occurrence of cracks of the image-forming material under a low humidity can be sometimes improved. That is, by lowering the Tg of the polymer, the occurrence of cracks of the image-forming material under a low humidity can be prevented, but because the Tg is too lowered, the adhesive property of the image-forming material sometimes causes a problem, there is the optimum value in the Tg of the polymer. The preferred Tg of the polymer depends upon the kind of a low-molecular compound used together, but is generally from 15xc2x0 C. to 120xc2x0 C., and preferably from 20xc2x0 C. to 80xc2x0 C.
Also, the occurrence of cracks is remarkable under a low humidity, and in general cracking is frequently evaluated by the radius of rounding the image-forming material in a pipe form at a temperature of 25xc2x0 C. and a relative humidity of 10% RH at which a crack begins to occur, and the preferred value is not larger than 50 mm.
Furthermore, for the purpose of preventing the occurrence of cracking, a plasticizer can be used. Practically, the plasticizers described in Japanese Patent Application No. 2000-65238 can be preferably used.
Also, a matting agent, a lubricant, etc., cam be used and practically, the compounds described in Japanese Patent Application No. 2000-65238 can be preferably used.
When a base is added to the image-forming layer or the protective layer, an organic base is preferred and preferred examples of the organic base include guanidine derivatives (e.g., 1,3-diphenylguanidine, 1,3-dimethylguanidine, 1,3-dibutylguanidine, 1-benzylguanidine, and 1,1,3,3-tetramethylguanidine), aniline derivatives (e.g., aniline, p-t-butylaniline, N,N-dimethylaniline, N,N-dibutylaniline, and triphenylamine), alkylamine derivatives (e.g., tributylamine, octylamine, laurylamine, benzylamine, and dibenzylamine), and heterocyclic compounds (e.g., N,Nxe2x80x2-dimethylaminopyridine, 1,8-diazabicyclo[5,4,0]-7-undecene, triphenylimidazole, lutidine, and 2-picoline). The organic base is added in an amount of preferably from 1 to 50 mol %, and particularly preferably from 5 to 20 mol % to the composition represented by A of the formula (I).
When the image-forming material of the invention is utilized as an image-forming material of a photon mode system, the addition of a compound generating an acid by the action of a light becomes inevitable.
On the other hand, when the image-forming material of the invention is utilized for the image-forming material of a heat mode system, for aiming at obtaining a higher sensitivity, an acid-generating agent may be additionally added. As known acid-generating agents, there are the compounds described in xe2x80x9cImaging Organic Materialxe2x80x9d edited by Yuki (Organic) Electronics Material Kenkyu Kai, published by Bunshin Shuppan Sha (1997), pages 37 to 91, and the compounds described in the cited literatures described therein. Also, many of the photo-acid-generating agents described therein function as acid-generating agents upon heating.
In the case of adding a pigment, preferred examples of the pigment used in the invention include diatomaceous earth, talc, kaolin, burned kaolin, titanium oxide, silicon oxide, magnesium carbonate, calcium carbonate, aluminum hydroxide, and a urea-formalin resin.
As other additives, there are ultraviolet absorbents of benzophenone-base, benzotriazole-base, etc.; head abrasion and sticking inhibitors made of higher fatty acid metal salts such as zinc stearate, calcium stearate, etc.; waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, caster wax, etc., and they can be, if necessary, added to the image-forming material.
The support used for the image-forming material of the invention includes papers such as wood-free papers, baryta papers, coated papers, cast-coated papers, synthetic papers, etc.; polymer films such as the films of polyethylene, polypropylene, polyethylene terephthalate, polyethylene-2,6-naphthylene dicarboxylate, polyarylene, polyimide, polycarbonate, triacetyl cellulose, etc.; glasses, metal foils, nonwoven fabrics, etc.
When the image-forming material of the invention is used for the uses for forming transmission type images such as an OHP film, a plate-making film, etc., a transparent support is used, Also, for the plate-making film, a support having a small thermal expansion coefficient, having a good dimensional stability, and having no absorption in the photosensitive region of a PS plate is selected.
In the image-forming material of the invention, a means for forming images is carried out by heating or a light irradiation of a light to heat energy transforming property, that is, of a so-called heat mode. When the image formation is carried out by heating, as the heating method, a method of contacting with a heated block or plate, a method contacting with a heat roller or a heat drum, or a method of image-wise heating by a thermal head of a heat-sensitive printer is used, and when the image formation is carried out by a light irradiation, in addition to a method of irradiating by a halogen lamp or an infrared or far-infrared lamp heater, there are a method of irradiating a laser light, etc. When the image-forming material of the invention is used for a use of requiring a high resolution such as the use of a plate-making material, etc., a system of scanning exposing by a laser light is preferred. For forming images by a smaller thermal energy, the thermal image-forming material of the invention can be previously heated to a proper temperature. In the present invention, after carrying out image-wise heating by the above-described method, the image can be amplified by heating the whole surface of the image-forming material to a temperature of from 60 to 150xc2x0 C. (preferably, from 60 to 120xc2x0 C.).
In the case of forming images by a laser light irradiation, to transform the laser light to a thermal energy, it is necessary to incorporate a dye absorbing the light of the wavelength of the laser light into an image-forming material. As a laser light source, there are an excimer laser, an argon laser, a helium neon laser, a semiconductor laser, a glass (YAG) laser, a carbonic acid laser, a dye laser, etc., and in these lasers, a helium neon laser, a semiconductor laser, and a glass laser is useful laser light sources in the invention. In these lasers, a semiconductor laser is particularly useful because the device is small and inexpensive. The oscillation wavelengths of semiconductor lasers are usually from 670 to 830 nm. Accordingly, for the image-forming material of the invention of carrying out recording by these laser lights, dyes having the light absorption in the near-infrared spectral region are used. As the near-infrared dyes used in the invention include cyanine dyes, squliarium dyes, merocyanine dyes, oxonole dyes, phthalocyanine dyes, etc. Practical examples thereof are described, for example, in U.S. Pat. Nos. 4,973,572, 4,948,777, 4,950,640, 4,950,639, 4,948,776, 4,948,778, 4,942,141, 4,952,552, 5,036,040, and 4,912,083.
Then, synthesis examples of the compounds of the invention are shown below but the invention is not limited to them.